Wharton experts used machine learning to help uncover the secret formula for successful healthy habit formation, and it turned out there’s no one formula.

“There’s this widely spread rumor that it takes 21 days to form a habit,” says Katy Milkman, a Wharton professor of operations, information, and decisions. “You may have also heard it takes 90 days to form a habit. There are popular books that tout these numbers that don’t have a sound basis in research. What we find is there is no such magic number.”

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